Bioabsorbable marker having radiopaque constituents and method of using the same

ABSTRACT

A temporary bioabsorbable-radiopaque marker for use on an implantable endoprosthesis. The bioabsorbable-radiopaque marker is adapted to be disposed on or adjacent an implantable endoprosthesis in a body lumen for a predetermined amount of time until the bioabsorbable and radiopaque materials are absorbed or dispersed in the body.

BACKGROUND OF THE INVENTION

This invention relates generally to a bioabsorbable marker havingradiopaque constituents “bioabsorbable-radiopaque marker” for use on animplantable endoprosthesis such as a stent. The bioabsorbable markerincludes dispersable radiopaque constituents which are not bioabsorbableor degradable, but are excreted from the body or stored in the body.

Implantable endoprostheses including stents, stent-grafts, and graftsare used in percutaneous transluminal coronary angioplasty and in othermedical procedures to repair and support diseased or damaged arteriesand body lumens. Grafts are implanted to cover or bridge leaks ordissections in vessels. Stent-grafts are stents which generally have aporous coating attachment. Unsupported grafts are porous tubes which aretypically implanted by surgical cut-down.

In order to visualize the passage and placement of the implantableendoprosthesis in arteries and body lumens, many surgical procedures areperformed with the aid of fluoroscopic angiography. The surgicaldelivery device and implantable endoprosthesis may be visualized if theyare radiopaque and offer radiographic contrast relative to the body. Forexample, X-ray radiation may be used to visualize surgical deliverydevices and deployment of the implant in the body. Also, radiographiccontrast solution may be injected into the body lumen so that the lumenmay be seen in the fluoroscopic image.

In order for the Implantable endoprosthesis to be radiopaque, it must bemade from a material possessing radiographic density higher thansurrounding host tissue and have sufficient thickness to affect thetransmission of x-rays to produce contrast in the image. Reference ismade to the clad composite stent shown in U.S. Pat. No. 5,630,840. Animplantable endoprosthesis may be made of metals including tantalum, orplatinum having relatively high radiographic densities. Other metalssuch as stainless steel, superalloys, nitinol, and titanium having lowerradiographic densities may also be used. Reference is made toimplantable devices shown in U.S. Pat. Nos. 4,655,771; 4,954,126; and5,061,275.

An implantable polymeric endoprosthesis is generally radiolucent anddoes not possess sufficient radiographic density to be easily imaged byfluoroscopy. To improve the imaging of such polymeric materials,polymers may be mixed with radiopaque filler materials prior to moldingor extruding in order to enhance the radiographic density. However, adisadvantage of using fillers with polymers is that changes in theproperties of the polymer may occur. For example, the additions offillers may reduce the strength or ductility of the polymer.

There is a need for an improved bioabsorbable-radiopaque marker for usein medical devices, particularly in temporary medical devices having lowradiopacity. The need to improve the radiopacity of a relatively lowradiopaque implantable endoprosthesis or to improve imaging in lowradiopaque conditions is particularly important for surgery,micro-surgery, neuro-surgery, and conventional angioplasty proceduresperformed under fluoroscopy. Physicians are constantly being challengedto place small implants at specific intraluminal locations. Variousdevices having radiopacity are known in the art such as shown in U.S.Pat. Nos. 4,447,239; 5,354,257; and 5,423,849.

All documents cited herein, including the foregoing, are incorporatedherein by reference in their entireties for all purposes.

SUMMARY OF THE INVENTION

Accordingly, there is a need for bioabsorbable-radiopaque markers foruse on implantable endoprostheses in order to improve radiopacity andthe locatability of an endoprosthesis during various medical procedures.Providing temporary radiopacity is especially advantageous forimplantable endoprostheses having little or no radiopacity. Thebioabsorbable-radiopaque markers allow radiographic identification ofone or more locations of interest on an implantable endoprosthesis.Bioabsorbable-radiopaque markers in the fabric or covering materials ofan implantable endoprosthesis are advantageous for indicating thelocation of the fabric or covering during implantation.

Alternative uses include threading the markers: adjacent a helicalstrand in the implantable endoprosthesis; circumferentially around theimplantable endoprosthesis; or in a straight line in the axial directionof the implantable endoprosthesis. One or more bioabsorbable-radiopaquemarkers may be used on the implantable endoprosthesis having little orno radiopacity. After implantation, the bioabsorbable-radiopaque markermay be absorbed, dissolved, or excreted from the body so as not toeffect the function of the endoprosthesis.

A disadvantage of certain permanent radiopaque markers is that they maycompromise structural integrity, may not be biocompatible or biostable,and may be more thrombogenic than the implantable endoprosthesis.

The bioabsorbable-radiopaque marker of the present inventionadvantageously allows most any implantable endoprosthesis to havetemporary radiopacity over a predetermined portion of its structure, andadvantageously assists with proper positioning and locatability of theimplantable endoprosthesis in a body lumen.

Use of the bioabsorbable-radiopaque marker is advantageous because theradiopaque property may be present only for a desired time period on animplantable endoprosthesis. For instance, once the implantableendoprosthesis is implanted, it may be more desirable to image withtechniques such as ultrasound, magnetic resonance, and endoscopy and toavoid further radiation exposure to the patient. As the bioabsorbablepolymer degrades, radiopaque material simultaneously or subsequentlydisperses into the body. The dispersion of the radiopaque material fromthe marker results in a loss of radiopacity in the marker. Apredetermined rate of release of the radiopaque material may be designedinto the bioabsorbable marker based on degradation of the polymer in thebody or the design of the marker structure.

The bioabsorbable material in the bioabsorbable-radiopaque markers mayinclude polymers or copolymers such as polylactide [poly-L-lactide(PLLA), poly-D-lactide (PDLA)], polyglycolide, polydioxanone,polycaprolactone, polygluconate, polylactic acid-polyethylene oxidecopolymers, modified cellulose, collagen, poly(hydroxybutyrate),polyanhydride, polyphosphoester, poly(amino acids), poly(alpha-hydroxyacid) or related copolymers materials, each of which have acharacteristic degradation rate in the body. For example, polyglycolideand polydioaxanone are relatively fast-bioabsorbing materials (weeks tomonths) and PLA is a relatively slow-bioabsorbing material (months toyears). For a PLA member, mass degradation is completed with totalabsorption of the polymer endoprosthesis in about 1.5 to 3 years afterimplantation.

Bioabsorbable resins such as PLLA, PDLA, PGA and others are commerciallvavailable from several sources including PURAC America, Inc. ofLincolnshire, Ill. Radiopaque materials such as barium sulfate andbismuth trioxide are commerciallv available and compounded with thebioabsorbable resin by New England Urethane, Inc. of North Haven, Conn.The bioabsorbable resin or bioabsorbable-radiopaque resin may beextruded into filament by Albany International Research Co. ofMansfield, Mass.

The bioabsorption rate of the marker may be designed to be fast forapplications where acute radiopacity is desired such as duringpositioning and placement of the implant. Alternatively, thebioabsorption rate may be designed to be slower for applications wherethe implant must be radiographically imaged for at least a portion ofits functional time, for example, in implants where healing may takemonths. Other bioabsorption rates are also possible. The bioabsorptionrate of the marker may be tailored by controlling the type ofbioabsorbable polymer; chemical composition of the bioabsorbablepolymer; molecular weight of the bioabsorbable polymer; thickness anddensity of the bioabsorbable polymer; surface area of the marker, exitarea for the radiopaque material, and design of the marker structure.

The degradation products from the bioabsorbable marker and the dispersedradiopaque material are metabolized, excreted, or stored by the body.Metabolism is the chemical process in living cells by which energy isprovided for vital processes and activities and new material isassimilated to repair the waste. It is the sum of the processes by whicha particular substance is handled in the living body. Excretion isseparation and elimination or discharge from the blood or tissues ofuseless, superfluous, or harmful material that is eliminated from thebody.

The biocompatibility of absorbable polymers during degradation dependsupon the rate of accumulation and how well the surrounding tissue orfluid buffers or metabolizes the degradation products. If the productsare metabolizable, the rate at which this will occur is dependent uponthe blood circulation in the tissue. A well-vascularized lumen wallcould buffer and metabolize degradation products as they are releasedfrom the implant. This biological process is important to minimizeadverse tissue reaction to the degrading implant.

The degradation products from PLLA and PGA are lactic and glycolic acid,respectively, which are normally present in the human body. The acidsare metabolized by cells around the implant. The metabolization processis a citrate cycle which converts the acids to carbon dioxide which isrespirated out of the body.

The radiopaque agents added to the bioabsorbable marker are generallyinsoluble in the body and thus are not metabolizable. If these materialsare trapped within tissue, the host generally reacts by encapsulationand acceptance of the biologically inactive particles. If the materialis released from the implant into systemic circulation, it will migratewith fluid flow until being excreted or collected and stored by organsor tissue. The idea is to only have small amounts of the radiopaquesubstances in the implant by incorporating the discretebioabsorbable-radiopaque marker rather than to load the entire implantwith the radiopaque material. Minimization of the amount of radiopaquematerial which will be liberated from the marker upon absorption of thepolymer must be considered when determining the loading percentage basedon radiographic and mechanical properties.

To be radiopaque, the markers should include material having atomicelements of sufficiently high atomic number and be of sufficientthickness to provide sufficient radiopacity for imaging. Thebioabsorbable-radiopaque marker may have one or more hollow, cavity, orporous portions wherein radiopaque material may be disposed.

Attenuation is the change in the number of photons in the incident x-raybeam due to the interaction with an absorber. To image an objectimplanted in the body, it would be desirable to have the objectattenuate x-rays more than body tissue, bone, and fat so that thedifference in contrast will be obvious in a radiograph. The difficultyin selecting a radiopaque material for surgical implants is that thematerial must have desirable radiographic characteristics andbiocompatibility.

In order to make an implant more radiopaque, a substance which absorbsmore x-rays can be deposited on or mixed in with the implant material.If the implant absorbs more x-rays than the surrounding medium (forexample tissue in the body), it will be visible as a sharp change incontrast on an x-ray film or fluoroscopy image.

The fraction of x-ray energy transmitted through the absorber isquantitatively predicted by the following equation described in ThePhysics of Radiology, Fourth Ed., H. Johns, J. Cunningham, 1983, pp.137-142.N=N ₀ e ^(−μx)

-   N=number of photons transmitted through x-   N₀=number of photons in the incident beam-   μ=linear attenuation coefficient of the absorber-   x=absorber thickness

N/N₀ would be the fraction of incident x-ray energy that is transmittedthrough the absorber. A more radiopaque material would have a lesserfraction of transmitted energy than a more radiolucent material.Therefore, to enhance the radiopacity of a material, such as the markermaterial, it would be desirable to select a material with high x-rayabsorbing capability to minimize the fraction of transmitted energy.This radiopacity capability is proportional to the linear attenuationcoefficient and the thickness of the absorber material. The higher theattenuation coefficient of the absorber material for a given thickness,the more radiopaque the absorber will be. The attenuation produced by anabsorber is dependent upon the number of electrons and atoms present inthe absorber. One way of quantifying this absorption characteristic iswith the atomic attenuation coefficient which is directly proportionalto the linear attenuation coefficient and the atomic number of theabsorber element. Radiopacity is therefore generally proportional to theatomic number (number of electrons in the atom) of the material.Candidate materials for enhancing the radiopacity of surgical implantswould have higher atomic numbers than the elements present in the bodyand would have to be biocompatible. The atomic number must besufficiently high so that relatively small thickness of absorbermaterial can be used in the body. Reference is also made to linearattenuation coefficient described in U.S. Pat. No. 5,628,787. Referenceis made to Table 1 which describes a number of elements and theirrespective atomic numbers and certain linear attenuation coefficients.TABLE 1 Element or Atomic Number or Linear Attenuation CoefficientMaterial Effective Atomic Number at 50 KeV, cm⁻¹ hydrogen 1 .000028carbon 6 .417 fat 6.46 .1925 water 7.51 .2245 muscle 7.64 .2330 air 7.78.00025 nitrogen 7 .00023 oxygen 8 .00028 bone 12.31 .5727 titanium 22iron 26 15.2 cobalt 27 18.8 bromine 35 zirconium 40 iodine 53 45 barium56 58 tantalum 73 111 platinum 78 108 gold 79 101 lead 82 88.7 bismuth83 108

The elements hydrogen, oxygen, carbon, and nitrogen are commonly foundin the body and in polymers, so elements with higher atomic numbers thanthese should enhance the radiopacity of a polymer implant or marker.Tantalum, zirconium, titanium, barium, bismuth, and iodine are known tobe non-toxic in certain concentrations and thus are candidate elementsfor enhancing radiopacity of a polymer marker in an implant. Theseelements can be added to the polymer in various loading percentages andthe threshhold above which the loading causes unsatisfactory changes inthe polymer characteristics can be determined through material anddevice testing. The elements which can be added in quantities sufficientto enhance radiopacity and maintain an acceptable level of polymerproperties and which are biocompatible could be utilized in markers. Thebiocompatible elements with a range of atomic numbers of from about 22to about 83 and having linear attenuation coefficients in the range offrom about 10 to about 120 cm⁻¹ at 50 KeV should provide enoughenhancement in radiopacity without excessive thickness being necessaryto be useful in markers. These elements would include at least titanium,vanadium, chromium, iron, cobalt, nickel, copper, bromine, zirconium,niobium, molybdenum, silver, iodine, barium, tantalum, tungsten,platinum, gold, and bismuth. The preferred metallic elements forbiocompatibility and radiopacity are titanium, zirconium, tantalum, andplatinum. The preferred organic elements for biocompatibility andradiopacity are bromine, iodine, barium, and bismuth. Especiallypreferred elements are tantalum, platinum, barium, and bismuth becauseof their high atomic numbers and biocompatibility (atomic numbers from56 to 83 and linear attenuation coefficients from 30 to 120). Tantalumand platinum are used as stent components and barium sulfate and bismuthtrioxide are used as radiopaque enhancements for polymer catheters.

The bioabsorbable-radiopaque marker may be integrated into a subassemblyor a finished implantable endoprosthesis during manufacture. Radiopaqueelongate elements may be braided together with non-radiopaquebioabsorbable elongate elements to form a tubular braided stent, or thebioabsorbable and radiopaque elongate elements may be woven into thefinished-braided stent.

The bioabsorbable-radiopaque marker would advantageously add temporaryradiopacity to an implantable endoprosthesis such that the temporarymarker would not require a medical procedure for removal from thepatient.

In sum the invention relates to an implantable endoprosthesis andbioabsorbable-radiopaque marker system including an implantableendoprosthesis adapted to be disposed in a body lumen and at least onemarker. The marker having a proximal end, a distal end, and a thickness.The marker including bioabsorbable material and radiopaque material andis disposed on or adjacent the endoprosthesis. The marker is adapted todegrade in vivo whereby the bioabsorbable material is metabolizedthrough or excreted from the body and the radiopaque material isexcreted from or stored in the body. The bioabsorbable material mayinclude a polymer or copolymer. The bioabsorbable material may includepoly-L-lactide, poly-D-lactide, polyglycolide, polydioxanone,polycaprolactone, and polygluconate, polylactic acid-polyethylene oxidecopolymers, modified cellulose, collagen, poly(hydroxybutyrate),polyanhydride, polyphosphoester, poly(amino acids), poly(alpha-hydroxyacid) and combinations thereof. The radiopaque material may have alinear attenuation coefficient of from about 10 cm⁻¹ at 50 KeV to about120 cm⁻¹ at 50 KeV. The marker may have an average thickness of fromabout 20 microns to about 500 microns and the radiopaque materialincludes at least one element with an atomic number of from about 22 toabout 83. The radiopaque material may include barium sulfate, bismuthtrioxide, bromine, iodine, iodide, titanium oxide, zirconium oxide,tantalum, and combinations thereof. The radiopaque material may be anoxide or salt material. One of the bioabsorbable material or radiopaquematerial may be coated or compounded with the other and the radiopaquematerial may have a linear attenuation coefficient of from about 10 cm⁻¹at 50 KeV to about 120 cm⁻¹ at 50 KeV. The marker may have a weightpercent of the radiopaque material in the bioabsorbable material of fromabout 1% to about 80%. The bioabsorbable material may consist of PLLAand the radiopaque material may consist of bismuth trioxide and theweight percent of the bismuth trioxide in the PLLA may be at least about10%. The bioabsorbable material may consist of PLLA and the radiopaquematerial may be barium sulfate and the weight percentage of the bariumsulfate in the PLLA may be at least about 10%. The marker maysubstantially degrades in less than about 3 years. “Substantialdegradadation of the marker” means that the marker has lost at least 50%of its structural strength. It is preferable that the marker lose about100% of its structural strength. The bioabsorbable material may consistof polylactide and the radiopaque material may consist of bariumsulfate, bismuth trioxide, iodine, iodide, and combinations thereof andthe marker substantially degrades in from about 1 year to about 2 years.The bioabsorbable material may include poly-L-lactide, poly-D-lactide,polyglycolide, and combinations thereof and the radiopaque material mayinclude barium sulfate, bismuth trioxide, bromine, iodine, iodide, andcombinations thereof and the marker substantially degrades in from about3 months to about 1 year. The bioabsorbable material may includepolyglycolide, polygluconate, polydioxanone, and combinations thereofand the radiopaque material may include barium sulfate, bismuthtrioxide, bromine, iodine, iodide, and combinations thereof and themarker substantially degrades in from about 1 week to about 3 months.The marker may be a mono-filament, multi-filament, thread, ribbon,suture, and combinations thereof. The marker may include one or morehollow, cavity, porous, and combinations thereof portions and theradiopaque material may be disposed therein. The marker may haveradiopacity for a predetermined amount of time. The endoprosthesis maybe a stent, stent-graft, graft, filter, occlusive device, or valve. Theendoprosthesis may have a tubular, radially expandable structure andaxially flexible structure including a plurality of the elongateelements which are interwoven in a braid-like configuration.

The invention also relates to an implantable endoprosthesis andbioabsorbable-radiopaque marker system including an implantableendoprosthesis adapted to be disposed in a body lumen and at least oneelongated marker. The marker is adapted to be disposed on or adjacentthe endoprosthesis. The marker includes a proximal end, distal end,thickness, bioabsorbable material, and a radiopaque material having alinear attenuation coefficient of from about 10 cm⁻¹ at 50 KeV to about120 cm⁻¹ at 50 KeV. The marker has at least one hollow, cavity, orporous portion where the radiopaque material may be disposed. Thebioabsorbable material at least partially contains the radiopaquematerial in the marker. The radiopaque material may be a liquid, solid,powder, gel, particle, or combinations thereof.

The invention also relates to a method of marking an implantableendoprosthesis including: disposing at least one elongate marker on oradjacent to at least a portion of an implantable endoprosthesis. Themarker is from about 20 weight percent to about 99 weight percent of abioabsorbable polymer and from about 1 weight percent to about 80 weightpercent of a radiopaque material. The radiopaque material includesliquid or particles, the particles having an average diameter less thanabout 200 microns and a maximum diameter less than about 400 microns.The radiopaque material has a linear attenuation coefficient of fromabout 10 cm⁻¹ at 50 KeV to about 120 cm⁻¹ at 50 KeV; disposing theendoprosthesis and marker in a delivery system; inserting the deliverysystem in a body lumen; deploying the endoprosthesis and marker from thedelivery system into a body lumen; and allowing the polymer to bioabsorbor excrete and the radiopaque material to subsequently or simultaneouslyat least partially disperses from the endoprosthesis.

The invention also relates to a temporary bioabsorbable-radiopaquemarker including a marker having an average thickness less than about500 microns and consisting of a bioabsorbable material and a radiopaquematerial, the radiopaque material having a linear attenuationcoefficient of from about 10 cm⁻¹ at 50 KeV to about 120 cm⁻¹ at 50 KeV.The marker is adapted to be disposed in a body lumen and degrade invivo. The marker may be elongate and have a proximal end and a distalend.

The invention also relates to a bioabsorbable-radiopaque markerincluding an elongate element adapted to be disposed in a body lumen andused as a surgical guide, the element including a bioabsorbablematerial, a radiopaque material, and combinations thereof. The elementhas a weight percent, W, of the radiopaque material in the bioabsorbablematerial, and an average thickness, T, over the length of the elongateelement. The weight percent, W, is equal to about:

-   -   (i) [10+((950×T(measured in mm))−208.5)]±5 for radiopaque        material having atomic weight 20-100;    -   (ii) ((950×T(measured in mm))−208.5)±5 for radiopaque material        having atomic weight of 100 to 150 up to a maximum of 80 weight        percentage; or    -   (iii) [((950×T(measured in mm))−208.5)−10]±5 for radiopaque        material having atomic weight greater than 150. The minimum W is        about 1 and the maximum W is about 80.

The invention also relates to a marker including from about 20 weightpercent to about 99 weight percent of a bioabsorbable polymer; and fromabout 1 weight percent to about 80 weight percent of a radiopaquematerial. The radiopaque material includes at least one of a liquid orparticle having an average particle diameter less than about 8 micronsand a maximum particle diameter less than about 10 microns. Theradiopaque material has a linear attenuation coefficient of from about10 cm⁻¹ at 50 KeV to about 120 cm⁻¹ at 50 KeV. For vascular system. Thepreferred average particle size is from about 3 microns to about 6microns and a maximum particle size of 6 microns. For the digestivesystem, the average particle size may be from about 100 microns to about150 microns and a maximum particle size of 400 microns.

Still other objects and advantages of the present invention and methodsof construction of the same will become readily apparent to thoseskilled in the art from the following detailed description, wherein onlythe preferred embodiments are shown and described, simply by way ofillustration of the best mode contemplated of carrying out theinvention. As will be realized, the invention is capable of other anddifferent embodiments and methods of construction, and its severaldetails are capable of modification in various obvious respects, allwithout departing from the invention. Accordingly, the drawing anddescription are to be regarded as illustrative in nature, and not asrestrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of stent delivery system having abioabsorbable-radiopaque marker disposed on an implantableendoprosthesis;

FIG. 2 is a side view of the delivery system and a deployed implantableendoprosthesis in a body lumen;

FIGS. 3 a, 3 b, and 3 c are cross-sectional views of three alternativemarker dispositions of the bioabsorbable-radiopaque marker on theimplantable endoprosthesis at section 3-3 of FIG. 2;

FIG. 4 is a side view of a bioabsorbable-radiopaque marker disposed in alongitudinal pattern on a implantable endoprosthesis;

FIG. 5 is a side view of a bioabsorbable-radiopaque marker disposed in ahelical pattern on a implantable endoprosthesis;

FIG. 6 is a side view of a relatively flexible bioabsorbable-radiopaquemarker;

FIGS. 7 a-7 e are cross-sectional views of five alternativebioabsorbable-radiopaque markers at section 7-7 of FIG. 6;

FIGS. 8 a-8 c are side views of three alternativebioabsorbable-radiopaque markers;

FIG. 9 is a side views of a porous bioabsorbable-radiopaque marker; and

FIGS. 10 a-10 d are side views of four elongate elements havingradiopaque materials therein.

FIG. 11 is a side view illustrating one possible arrangement of discretebioabsorbable-radiopaque markers disposed on an implantableendoprosthesis;

FIG. 12 is the detail bounded by the dashed-line circle in FIG. 12illustrating a bioabsorbable-radiopaque marker disposed around oneimplantable endoprosthesis wire crossing point;

FIG. 13 is a side view illustrating a discrete radiopaque marker; and

FIG. 14 illustrates the discrete bioabsorbable-radiopaque markerpositioned on an embolization occlusion coil intravascular device.

DETAILED DESCRIPTION OF THE INVENTION

Reference is made to FIG. 1 illustrating a stent delivery device 10having one or more bioabsorbable-radiopaque markers 14 disposed in ahelical pattern on an implantable endoprosthesis 16. Thebioabsorbable-radiopaque marker 14 is disposed on the endoprosthesis 16preferably before loading the assembly thereof into the outer tube of adelivery device 10. Reference is made to a delivery device shown in U.S.Pat. No. 5,026,377.

FIG. 2 illustrates an implantable endoprosthesis 16 having abioabsorbable-radiopaque markers 14 disposed in a helical patternthereon in a body lumen 12. Implantable endoprostheses 16 known in theart include stents, stent-grafts, grafts, filters, occlusive devices,valves, and combinations thereof, all may incorporate thebioabsorbable-radiopaque marker 14.

FIGS. 3 a-3 c illustrate three alternative locations on an implantableendoprosthesis 16 for disposing the bioabsorbable-radiopaque marker. Thebioabsorbable-radiopaque marker 14 may be disposed on portions of theinside surface 17, outside surface 19, or be inter-woven orinter-braided about and through the elongated elements of theimplantable endoprosthesis 16. The bioabsorbable-radiopaque marker 14may be disposed on the implantable endoprosthesis 16 in one or morepredetermined lengths.

Reference is made to FIGS. 4 and 5 illustrating thebioabsorbable-radiopaque marker 14 disposed in two alternative patternson the implantable endoprosthesis 16. FIG. 4 shows thebioabsorbable-radiopaque marker 14 interwoven through the filaments ofthe endoprosthesis 16 in a relatively longitudinal pattern.Alternatively, the bioabsorbable-radiopaque marker 14 may be interwoventhrough the filaments of the endoprosthesis 16 in a relativelycircumferential pattern. FIG. 5 shows a marker 14 interwoven through thefilaments of the endoprosthesis 16 in a relatively helical pattern.Other patterns and dispositions of the bioabsorbable-radiopaque marker14 on the endoprosthesis 16 are also possible. One or more markers 14may be temporarily disposed on the implantable endoprosthesis 16 toadvantageously provide temporary radiopacity to predetermined locationson the implantable endoprosthesis 16.

As shown in FIGS. 3 a and 3 c, the bioabsorbable-radiopaque marker 14may be disposed to one or more surfaces of the implantableendoprosthesis 16 with a relatively weak bioabsorbable adhesive orgelatin.

The bioabsorbable-radiopaque marker 14 may include elongate elementssuch as a ribbon, thread, filament, suture, or combinations thereof. Thebioabsorbable-radiopaque marker 14 may be braided to form a rope orcable.

As the implantable endoprosthesis 16 is deployed from the deliverydevice 10, the bioabsorbable-radiopaque marker 14 may adjust with theexpansion of the implantable endoprosthesis 16, and advantageouslyprovide radiopacity and enhance the viewing of the implantableendoprosthesis 16 position or size during fluoroscopy. Once theimplantable endoprosthesis 16 is fully deployed, the delivery device 10may be removed from the body and the bioabsorbable-radiopaque marker 14may remain on the implantable endoprosthesis 16 to be bioabsorbed,dissolved, dispersed, or excreted from the body. Thebioabsorbable-radiopaque marker 14 may be designed to remain on theimplantable endoprosthesis 16 for a predetermined period of time ifthere is a need for follow-up angiography.

Reference is made to FIG. 6 illustrating a bioabsorbable-radiopaquemarker 14 preferably made from a relatively flexible elongate polymericmaterial including radiopaque material containing at least one elementwith an atomic number of from about 22 to about 83. The radiopaquematerial preferably has a linear attenuation coefficient of from about10 cm⁻¹ at 50 KeV to about 120 cm⁻¹ at 50 KeV.

FIGS. 7 a-7 e illustrate alternative cross-sectional embodiments of thebioabsorbable-radiopaque marker 14 taken through the line 7-7 of FIG. 6.FIG. 7 a shows a substantially solid member; FIG. 7 b shows a hollowmember; FIG. 7 c shows a member having pores extending radially into themember; FIG. 7 d shows a rectangular or ribbon member; and FIG. 7 eshows a braided hollow member. FIG. 7 e may also be a substantiallysolid braided member.

A composite bioabsorbable-radiopaque marker 14 may include abioabsorbable polymer that is coated, compounded, filled, loaded, ormixed with a radiopaque substance such as iodide, iodine, zirconiumoxide, barium sulfate, bismuth trioxide, or a related oxide or saltsubstance. Composite radiopaque materials may contain at least oneelement having an atomic number, preferably, higher than about 22. Otherradiopaque materials may include gold, platinum, tantalum, metallicbiomaterial alloys for coating, and small particles of these materials,preferably, less than 10 microns in size for compounding. Forcompounding radiopaque constituents and bioabsorbable resins to makeextruded bioabsorbable-radiopaque filament, the weight percentage ofradiopaque resins to bioabsorbable resins ranges from about 1 percent toabout 80 percent. For compounding radiopaque metallic fillers andbioabsorbable resins to make extruded bioabsorbable-radiopaque filament,the weight percentage of radiopaque metallic fillers to bioabsorbableresins ranges from about 1 percent to about 40 percent. The preferredweight percentage of bismuth trioxide and barium sulfate in PLLAfilament is a minimum of about 10%. Preferred embodiments of thebioabsorbable-radiopaque marker are set forth below in Table 2. TABLE 2Metal Organic Preferred Preferred Preferred Radiopaque PreferredRadiopaque Marker Matrix Marker Matrix Marker Metal Constituent MarkerOrganic Constituent Materials For Materials For Radiopaque Loading,Radiopaque Loading, Fast Slow Marker Type Function Devices ConstituentsWeight % Constituent Weight % Absorption Absorption threading on markoverall braided tubular Ti, Ta, Zr, Pt Ti, Zr = 15-40 Br, I, Ba, Bi Br,I = 40-80 PGA, PLLA, PDLA helix stent length, stents, filters, Ta, Pt =1-20 Bi, Ba = 10-80 polydioxanone location in occlusion, vessel valvesthreading mark stent braided tubular Ti, Ta, Zr, Pt Ti, Zr = 15-40 Br,I, Ba, Bi Br, I = 40-80 PGA, PLLA, PDLA around ends, location stents,filters, Ta, Pt = 1-20 Bi, Ba = 10-80 polydioxanone circum- in vessel,occlusion, ference covering valves, stent length, grafts expansionthreading on mark overall braided tubular Ti, Ta, Zr, Pt Ti, Zr = 15-40Br, I, Ba, Bi Br, I = 40-80 PGA, PLLA, PDLA straight axial stent length,stents, filters, Ta, Pt = 1-20 Bi, Ba = 10-80 polydioxanone linelocation in occlusion, vessel valves, stent grafts pigtail rings markstent braided tubular Ti, Ta, Zr, Pt Ti, Zr = 15-40 Br, I, Ba, Bi Br, I= 40-80 PGA, PLLA, PDLA ends or center, stents, filters, Ta, Pt = 1-20Bi, Ba = 10-80 polydioxanone location in occlusion, vessel, valves,stent expansion grafts coils mark stent braided tubular Ti, Ta, Zr, PtTi, Zr = 15-40 Br, I, Ba, Bi Br, I = 40-80 PGA, PLLA, PDLA ends orcenter, stents, filters, Ta, Pt = 1-20 Bi, Ba = 10-80 polydioxanonelocation in occlusion, vessel, valves, stent expansion grafts knots markstent braided tubular Ti, Ta, Zr, Pt Ti, Zr = 15-40 Br, I, Ba, Bi Br, I= 40-80 PGA, PLLA, PDLA ends or center, stents, filters, Ta, Pt = 1-20Bi, Ba = 10-80 polydioxanone location in occlusion, vessel, valves,stent expansion grafts

The column for marker type in Table 2 contains a description of thephysical aspects of the marker such as a strand threaded in and out ofthe braided stent interstices, following a wire helix or in and out ofthe braided stent interstices around the circumference, or in and out ofthe braided stent interstices in a straight line in the axialorientation. An interstice is the location where two stent wires in thebraid cross over one another. The function of the marker is described inTable 2 to indicate how the marker is used in the endoprosthesis, forexample, to indicate the ends of a stent or to allow radiographicvisualization of the stent changing from a constrained condition to anexpanded condition as it is deployed. A list of devices where the markercould be incorporated is provided in Table 2 and generally containsvarious types of intraluminal endoprostheses. The preferred metalradiopaque constituents (Ta, Pt, Zr, Ti) are known to be biocompatibleand have relatively high atomic numbers and linear attenuationcoefficients. These elements would be added to the bioabsorbable polymerto make the material radiopaque and suitable for radiographic marking.The adjacent column, Metal Radiopaque Constituent Loading, Weight %,indicates the preferred range of loading of the metal radiopaqueconstituents into the bioabsorbable polymer to make it sufficientlyradiopaque, such as from about 1 to about 20 weight percent tantalum orplatinum compounded or coated onto the polymer. The same type ofinformation is given in the next two columns for organic radiopaqueconstituents. The marker may be made with either metal or organicconstituents, with metal being preferred for thin markers and organicsbeing more appropriate for thicker markers where higher loadings can betolerated (so as to not weaken the marker significantly). The last twocolumns in the table contain preferred absorbable polymers for themarker matrix material. PLLA and PDLA are preferred for slow-absorbingmarkers, because the degradation rate of these polymers is rather slow(months to years). PGA and polydioxanone are preferred forfast-absorbing markers because the degradation rate of these polymers israther fast (weeks to months).

For description purposes, the markers of the invention can be segregatedinto types; threaded and discrete bioabsorbable-radiopaque markers. Athreaded marker is generally a strand or strands of material havingradiopacity which is incorporated within the implantable device byinterweaving or interbraiding the strand through the struts or wires ofthe endoprosthesis. A discrete bioabsorbable-radiopaque marker isgenerally a bioabsorbable-radiopaque polymer strand of material which issecurely attached to a localized region of the implantable device anddoes not significantly extend over a large portion of the device.

An example of a threaded marker in a braided wire tubular stent is abioabsorbable-radiopaque polymer strand loaded with a radiopaqueconstituent that is woven in and out of the wire crossing pointsfollowing the helical path of one individual wire strand in the stent.

An example of a discrete bioabsorbable-radiopaque marker is a coil,knot, or ring of a bioabsorbable-radiopaque polymer strand around afeature of a stent, such as a stent wire crossing point. The strand iswrapped, coiled, or tied around the stent wire and thereby ismechanically attached to the device. The strand ends are clipped offsuch that the marker is present as a small, tight ring around a featureof the stent. The stent with the attached markers is loaded and deployedfrom the delivery.

The absorbable radiopaque markers are used in a variety of intraluminalendoprostheses such as stents, grafts, filters, occlusive devices, andvalves. The endoprostheses are implanted in airways, the digestivesystem, and the vascular system. When the markers are implanted andexposed to body fluids the absorbable polymer matrix undergoesdegradation and eventually disintegrates releasing the nondegradableradiopaque constituents into the body. If the endoprosthesis and markershave been fully incorporated in the vessel wall, the radiopaquesubstances will be contained within the local tissue (as with a stent).If the endoprosthesis and markers are not ingrown and incorporated, theradiopaque substances may be released into the body fluid. The releaseis of little concern in the digestive system, because the smallconcentration of particles liberated are likely to have little affect onbile and would be quickly excreted. The release of particles into thevascular system is less desirable but this can be avoided by using lowloading percentages and fine particle sizes for vascular deviceindications.

The function of the absorbable threaded radiopaque marker is to indicateon a radiographic image the location of the stent within the treatmentsite and the length of the expanded stent can be determined by measuringthe length of the marker as it follows the stent shape if the marker wasthreaded along a stent wire helix or axially along a line in the stent.The marker can be threaded circumferentially at each end of the stentcovering in a covered stent or stent-graft to indicate the location ofthe radiolucent covering material. The stent expansion during deploymentcan be observed radiographically by watching the radiopaque markerhelical or circumferential strand open up as the self-expanding stent isreleased from its radially constrained state.

Discrete bioabsorbable-radiopaque markers have the same functionalpurpose as the threaded markers, but they can be more easily used tomark the specific locations of features of interest on the stent. Forexample, a discrete bioabsorbable-radiopaque marker can be added to thecenter of the stent length to aid the physician in centering the stentwithin the stricture. Discrete bioabsorbable-radiopaque markers could beused to attach covering fabrics or films to stents to make stent graftsso that the location of the covering on the stent could be determinedradiographically.

The discrete bioabsorbable-radiopaque markers can be made frombiocompatible absorbable polymers containing elements with relativelyhigh atomic numbers such as titanium, tantalum, zirconium, and platinum.The radiopaque elements can be added by metallurgically alloying or bymaking clad composite structures. Radiopaque constituents may be filledinto hollow cores, cavities or pores in the polymer matrix. Organicradiopaque powders containing elements or salts or oxides of elementssuch as bromine, iodine, iodide, barium, and bismuth could be usedinstead of metal powders.

The amount of radiopaque constituent that is added to the absorbablepolymer matrix is generally from about 1-80 weight percent, but thespecific loading depends upon the atomic number of the radiopaqueconstituent and the thickness of the marker. Metallic elements liketantalum and platinum which have high atomic numbers can be loaded insmall percentages (about 1-20 weight percent) while metallic elementswith lower atomic numbers such as titanium and zirconium have to beloaded in higher percentages (about 20-40%). Organic radiopaqueconstituents with relatively low atomic numbers like iodine and brominerequire loading percentages of from about 40-80 weight percent whileorganics with higher atomic numbers could be as low as 10% in thickmarkers. It is desirable to have the radiopaque constituent particlesize be less than 10 microns so that when dispersed into the body theparticles will not be so large as to cause obstruction or embolization.

EXAMPLE 1

An absorbable threaded radiopaque marker can be in the form of a strandof poly (α-hydroxy acid) polymer containing radiopaque elements, oxides,or salts of elements with atomic numbers of from about 22 to about 83interwoven or interbraided along a helical, circumferentail, or axialorientation on an endoprosthesis such as a stent, stent-graft, graft,filter, occlusive device, and valve. The radiopaque material has alinear attenuation coefficient of from about 10 cm⁻¹ at 50 KeV to about120 cm⁻¹ at 50 KeV.

EXAMPLE 2

An absorbable threaded radiopaque marker can be in the form of a strandof poly (α-hydroxy acid) polymer containing radiopaque elements, oxides,or salts of elements with atomic numbers of from about 22 to about 83disposed on one or more surfaces of an endoprosthesis such as a stent,stent-graft, graft, filter, occlusive device, and valve. The radiopaquematerial has a linear attenuation coefficient of from about 10 cm⁻¹ at50 KeV to about 120 cm⁻¹ at 50 KeV.

EXAMPLE 3

An absorbable threaded radiopaque marker can be in the form of a strandof poly (α-hydroxy acid) polymer containing radiopaque elements withatomic numbers of from about 22 to about 83, loaded into hollow cores,cavities, or pores of the polymer portion and disposed on anendoprosthesis such as a stent, stent-graft, graft, filter, occlusivedevice, and valve. The radiopaque material has a linear attenuationcoefficient of from about 10 cm⁻¹ at 50 KeV to about 120 cm⁻¹ at 50 KeV.

EXAMPLE 4

An absorbable threaded radiopaque can be a coated or clad compositemarker strand of poly (α-hydroxy acid) polymer and radiopaque metallicelements with atomic numbers of from about 22 to about 83, preferablytitanium, tantalum, zirconium, and disposed on an endoprosthesis such asa stent, stent-graft, graft, filter, occlusive device, and valve. Theradiopaque material has a linear attenuation coefficient of from about10 cm⁻¹ at 50 KeV to about 120 cm⁻¹ at 50 KeV.

EXAMPLE 5

An absorbable threaded radiopaque marker can be in the form of a strandof poly (α-hydroxy acid) polymer monofilament, ribbon, or multifilamentwire containing radiopaque metallic elements with atomic numbers of fromabout 22 to about 83, preferably compounded or coated with titanium,tantalum, zirconium, and platinum metal powders or bromine, iodine,iodide, barium, and bismuth element, oxides or salts disposed on anendoprosthesis such as a stent, stent-graft, graft, filter, occlusivedevice, and valve. The radiopaque material has a linear attenuationcoefficient of from about 10 cm⁻¹ at 50 KeV to about 120 cm⁻¹ at 50 KeV.

EXAMPLE 6

An absorbable threaded radiopaque marker can be in the form of poly(α-hydroxy acid) polymer matrix composite strand containing radiopaquemetallic elements with atomic numbers of from about 22 to about 83,preferably titanium, tantalum, zirconium, and platinum metal powders orbromine, iodine, iodide, barium, and bismuth element, oxides or saltpowders disposed on an endoprosthesis such as a stent, stent-graft,graft, filter, occlusive device, and valve. The radiopaque material hasa linear attenuation coefficient of from about 10 cm⁻¹ at 50 KeV toabout 120 cm⁻¹ at 50 KeV.

EXAMPLE 7

A discrete bioabsorbable-radiopaque marker can be in the form of poly(α-hydroxy acid) polymer containing radiopaque metallic elements withatomic numbers of from about 22 to about 83, preferably titanium,tantalum, zirconium, and platinum attached by wrapping, coiling, ortying around features within an endoprosthesis such as a stent,stent-graft, graft, filter, occlusive device, and valve such that themarker is attached and bioabsorbably removable from the endoprosthesis.The radiopaque material has a linear attenuation coefficient of fromabout 10 cm⁻¹ at 50 KeV to about 120 cm⁻¹ at 50 KeV.

Reference is made to FIGS. 8 a-8 c illustrating alternative embodimentsof a portion of a bioabsorbable-radiopaque marker 14. Thebioabsorbable-radiopaque marker 14 may have at least one portion fortemporary containment of a radiopaque material. The radiopaque materialmay be disposed in one or more hollow, cavity or pore portions in themarker 14. For example. FIG. 8 a shows a solid bioabsorbable-radiopaquemarker 14. As shown in FIGS. 8 b-8 c, the bioabsorbable-radiopaquemarker 14, may receive a radiopaque core 13 disposed in the once hollow15 portion. The radiopaque core 13 may be slowly released from the openends 14 a, 14 b of the hollow portion 15 into the body. Alternatively,the radiopaque core 13 may be released from the radiopaque core 13through pores in the walls of the marker 14 into the body.

FIG. 9 is an illustration of a bioabsorbable-radiopaque marker 14 havingpores 35. The pores may connect to a reservoir of radiopaque material ina cavity 25 or hollow 15 area or he individual pores 35 may be filledwith radiopaque material. The pores 35 allow the radiopaque materialdisposed in the marker 14 to exit from the marker 14 over a period oftime.

The radiopaque material may be solid or include a bioabsorbable casingsurrounding a liquid, solid, gel, powder, or combination thereof and beheld in place in a hollow portion 15, cavity 25, or porous 35 portion bya relatively weak bioabsorbable adhesive, bioabsorbable gelatin,friction, or by other mechanical or chemical means known in the art. Theradiopaque material may be designed to disperse from thebioabsorbable-radiopaque marker 14 after a predetermined period of time.The radiopaque material preferably has at least one element with anatomic number of from about 22 to about 83 and is removably-attachablein at least one hollow 15, cavity 25, or porous 35 portions in themarker 14. The bioabsorbable-radiopaque marker 14 may further compriseone or more walls 30 including walls between hollow 15, cavity 25, andporous 35 portions, proximal and distal walls, and combinations thereofthat are adapted to bioabsorb in vivo.

Reference is made to FIGS. 10 a-10 d illustrating different embodimentsof the bioabsorbable-radiopaque marker 14 having hollow 15, cavity 25,porous 35 portions, or combinations thereof filled with a non-toxicradiopaque material. FIG. 10 a shows a bioabsorbable-radiopaque marker14 with a hollow 15 portion filled with radiopaque material and havingat least one of the proximal or distal ends open; FIG. 10 b shows abioabsorbable-radiopaque marker 14 with a cavity 25 portion filled withradiopaque material having closed ends; FIG. 10 c shows abioabsorbable-radiopaque marker 14 with porous 35 portions filled withradiopaque material; and FIG. 10 d shows a bioabsorbable-radiopaquemarker 14 with combinations of hollow 15, cavity 25, and porous 35portions filled with radiopaque material. The bioabsorbable-radiopaquemarker 14 reacts with body fluids and decomposes and then theconstituents are absorbed or excreted from the body.

FIG. 11 illustrates discrete bioabsorbable-radiopaque markers 14 made byforming small rings or coils of bioabsorbable-radiopaque filament aroundfeatures of the implantable endoprosthesis 16. Relatively small anddiscrete filament loops (pigtail) bioabsorbable-radiopaque markers 14are shown at the wire crossing points on the tubular braid.

FIG. 12 illustrates the detail bounded by the dashed-line circle in FIG.11 showing a bioabsorbable-radiopaque marker 14 around one implantableendoprosthesis 16 wire crossing point.

FIG. 13 illustrates the bioabsorbable-radiopaque marker 14 of FIG. 12and FIG. 13 and shows filament ends 14 a, 14 b which simply pass overeach other to form an enclosed loop that is further preferably knotted,twisted, or tied at ends 14 a, 14 b. The bioabsorbable-radiopaquemarkers 14 may be relatively small and comprise a single loop or pigtailof filament around one filament crossing point, filament, anembolization coil, or the like. The bioabsorbable-radiopaque marker 14is preferably made of a PGA, Polydioxanone, PLLA, PDLA, or combinationsthereof. Biocompatible radiopaque metal constituents preferably includetitanium, zirconium, tantalum, and platinum. Preferred organicradiopaque constituents include bromine, barium, bismuth, iodine, orcombinations thereof.

The bioabsorbable-radiopaque marker 14 is preferably formed from anelongate member such as a filament and shaped accordingly onto theimplantable endoprosthesis 16. The bioabsorbable-radiopaque marker 14advantageously allows custom marking of the implantable endoprosthesis16 without the need to acquire preformed marker bands or to devise acomplicated manufacturing operation. The bioabsorbable-radiopaquemarkers 14 may be easily and quickly added to the implantableendoprosthesis 16. Also, only small, specific sites are marked by thebioabsorbable-radiopaque marker 14 so a minimum amount of foreign bodymaterial would be added to the implantable endoprosthesis 16.

The bioabsorbable-radiopaque markers 14 should preferably be smallerthan the size of the element in the implantable endoprosthesis 16. Asmaller diameter bioabsorbable-radiopaque marker 14 should fit throughmost weaves, be deformable, and may be cut to size.

Reference is made to FIGS. 12-13 illustrating discretebioabsorbable-radiopaque markers 14 looped one or more times about afilament or filament crossing point to prevent release therefrom. Theends 14 a, 14 b are clipped and positioned to lie in a plane parallel tothe longitudinal axis of the implantable endoprosthesis 16. Thebioabsorbable-radiopaque marker 14 may be disposed on one or morefilament crossing or every other filament crossing point around thecircumference of the braid in one circular transverse plane. Thebioabsorbable-radiopaque markers 14 may be positioned to form one ormore circumferential rings on the implantable endoprosthesis 16.Alternatively, the bioabsorbable-radiopaque markers 14 may be positionedalong an embolization occlusion coil intravascular device or filament atpredetermined locations as illustrated in FIG. 15. The ends 14 a, 14 bmay then be tied, twisted, knotted, or adhesively connected together andthereafter clipped and positioned to lie in an unobtrusive low-profileposition.

It will be evident from considerations of the foregoing that thebioabsorbable-radiopaque marker 14 may be constructed using a number ofmethods and materials, in a wide variety of sizes and styles for thegreater efficiency and convenience of a user.

A bioabsorbable marker that may advantageously be used in conjunctionwith the present invention is disclosed in J. Stinson's and ClaudeClerc's U.S. patent application entitled “Radiopaque Markers And MethodsOf Using Same”, Ser. No. ______ , filed concurrently herewith, andcommonly assigned to the assignee of this application.

A bioabsorbable stent that may advantageously be used in conjunctionwith the present invention is disclosed in J. Stinson's U.S. patentapplication entitled “Bioabsorbable Implantable Endoprosthesis WithReservoir And Method Of Using Same”, Ser. No. ______; filed concurrentlyherewith, and commonly assigned to the assignee of this application.

Another bioabsorbable stent that may advantageously be used inconjunction with the present invention is disclosed in J. Stinson's U.S.patent application entitled “Bioabsorbable Self-Expanding Stent”, Ser.No. ______, filed concurrently herewith, and commonly assigned to theassignee of this application.

The above described embodiments of the invention are merely descriptiveof its principles and are not to be considered limiting. Furthermodifications of the invention herein disclosed will occur to thoseskilled in the respective arts and all such modifications are deemed tobe within the scope of the invention as defined by the following claims.

1-46. (canceled)
 47. A method, comprising: imaging a medical device withX-rays, the medical device having a first radiopacity; and imaging themedical device with a magnetic field, the medical device having a secondradiopacity less than the first radiopacity.
 48. The method of claim 47,wherein the medical device comprises a biodegradable composition. 49.The method of claim 48, wherein the biodegradable composition is in theform of a coating.
 50. The method of claim 47, wherein the medicaldevice is imaged with the magnetic field after imaging the medicaldevice with X-rays.
 51. The method of claim 47, further comprisingimplanting the medical device.
 52. The method of claim 51, wherein themedical device is imaged with the magnetic field after implanting themedical device.
 53. The method of claim 47, wherein the medical devicecomprises an endoprosthesis.
 54. The method of claim 53, wherein themedical device comprises a stent.
 55. The method of claim 53, whereinthe endoprosthesis comprises a polymer.
 56. The method of claim 47,wherein the medical device comprises an occlusive device.
 57. A method,comprising: imaging a medical device with a first imaging technique;changing the visibility of the medical device, as imaged by the firstimaging technique; and imaging the medical device with a second imagingtechnique different than the first imaging technique.
 58. The method ofclaim 57, wherein the first imaging technique comprises applying X-rays.59. The method of claim 57, wherein the second imaging technique isselected from the group consisting of ultrasound, magnetic resonance,and endoscopy.
 60. The method of claim 57, wherein the medical devicecomprises a biodegradable composition.
 61. The method of claim 60,wherein the biodegradable composition is in the form of a coating. 62.The method of claim 57, wherein the medical device is imaged with thesecond imaging technique after imaging the medical device with the firsttechnique.
 63. The method of claim 57, further comprising implanting themedical device.
 64. The method of claim 63, wherein the medical deviceis imaged with the second technique after implanting the medical device.65. The method of claim 57, wherein the medical device comprises anendoprosthesis.
 66. The method of claim 65, wherein the medical devicecomprises a stent.
 67. The method of claim 65, wherein theendoprosthesis comprises a polymer.
 68. The method of claim 57, whereinthe medical device comprises an occlusive device.
 69. An implantablemedical device, comprising a radiopaque composition capable ofdiminishing in radiopacity after the device has been implanted in abody.
 70. The device of claim 69, wherein the composition isbiodegradable.
 71. The device of claim 70, wherein the composition is inthe form of a coating.
 72. The device of claim 69, wherein the medicaldevice comprises an endoprosthesis.
 73. The device of claim 72, whereinthe medical device comprises a stent.
 74. The device of claim 72,wherein the endoprosthesis comprises a polymer.
 75. The device of claim69, wherein the medical device comprises an occlusive device.